This invention relates to a process for removing naphthenic acids from petroleum distillate and the like. In a further aspect, the present process affords the recovery of relatively high purity naphthenic acids. In another aspect, the invention relates to an extraction solvent system comprising methanol, ammonium hydroxide, and water in certain critical ratios.
Crude petroleum oil and distilled fractions thereof contain appreciable amounts of naphthenic acids. These acids are useful materials, having been used to solubilize metal ions, form detergents, and the like. Furthermore, naphthenic acids are a problem in refinery operations where they cause corrosion of the metal vessels used for storage and distillation. Numerous processes have been proposed for removing naphthenic acids from hydrocarbon streams. However, to date an effective method for recovering essentially all of the naphthenic acid from a distilled hydrocarbon fraction in high purity has not been developed.
U.S. Pat. No. 2,769,768, assigned to Pure Oil Company, claims a process for extracting naphthenic acids from hydrocarbons by contacting them with a solvent comprising methanol; at least one other aliphatic, low molecular weight alcohol; and a basic agent. The preferred basic agent is ammonia.
U.S. Pat. No. 2,808,431, assigned to Pure Oil Company, teaches a process to remove high molecular weight naphthenic acids from hydrocarbons by contacting them with a two-phase mixture of a volatile, nonpolar organic liquid and a polar liquid. Typical nonpolar materials are low molecular weight aliphatic hydrocarbons; typical polar materials are volatile, low molecular weight alcohols containing minor amounts of ammonia and water. By minor amounts are meant less than 11 percent by volume of water and between 0.5-5 percent by volume base as ammonium hydroxide.
U.S. Pat. No. 2,850,435, assigned to Pure Oil Company, describes a process and a new solvent combination for the extraction of high molecular weight naphthenic acids from hydrocarbons. The solvent system of this patent is an anhydrous methanol containing 1-15 percent ammonia. Data is presented to show that the inclusion of water causes a decrease in the efficiency of the extraction. However, the highest water concentration examined was only 12 percent.
U.S. Pat. No. 2,911,360, assigned to Sun Oil Company, discloses a process for removing naphthenic acids from petroleum crudes or reduced crudes which comprises contacting the crude with 30-50 percent aqueous alcohol in the presence of a basic material (e.g., alkali metal hydroxides, ammonia, and organic amines), followed by vapor phase treatment.